1. Technical Field of the Invention
The present invention relates to an image forming apparatus used for multicolor image forming, and particularly to an image forming apparatus in which a transfer medium is electrostatically adsorbed onto a dielectric screen of a transfer medium supporting member for repeated image transfer operations so that toner images successively formed on a photoconductive member can be transferred to the same transfer medium one over another.
2. Brief Description of the Prior Art
Such a kind of conventionally known apparatus is disclosed in a Japanese Unexamined Publication No. 90673/1987. In this apparatus, by electrifying a dielectric screen of a transfer medium supporting member by corona discharge of an adsorption charger, a transfer medium is electrostaticly adsorbed onto the dielectric screen through the electrostatic adsorptive power of the dielectric screen to be supported thereon in a wound state, and is subjected to an image transfer operation. After the transfer operation is completed, the dielectric screen is de-electrified by corona discharge so as to separate the transfer medium therefrom, and thereby the transfer medium carrying a transferred image thereon can be surely delivered to the next step of operation. As the abovementioned dielectric screen, a mesh screen such as a polyester or nylon screen, or a film screen such as a polyester film is used.
However, if the dielectric screen is used for a long time and repeatedlys ubjected to the electrification and de-electrification by corona discharge, toner, papar powder, charged products and the like are attached to the surface of the dielectric screen and the dielectric screen is unevenly deformed thereby disadvantageously lowering the electrification capacity of the dielectric screen. As a result, the electrostatic adsorption of a transfer medium onto the dielectric screen and the release of the same from the adsorbed state are performed only insufficiently, and jamming of the transfer medium, unsatisfactory image transfer or ill separation of the transfer medium are caused.